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Beam dump induced background in EAR-2

Expectations from FLUKA simulations. Beam dump induced background in EAR-2. Ida Bergström Luleå Tekniska Universitet (SE) Vasilis Vlachoudis , CERN. OUTLINE Estimated background contributions in EAR-2 from the collimator and from backscattering.

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Beam dump induced background in EAR-2

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  1. Expectations from FLUKA simulations Beam dump induced background in EAR-2 Ida BergströmLuleåTekniskaUniversitet (SE) VasilisVlachoudis, CERN

  2. OUTLINE • Estimated background contributions in EAR-2 from the collimator and from backscattering. • Optimization of the beam dump in order to reduce the backscattering of neutrons and photons • Different designs • Summary tables, plots

  3. BACKGROUND MEASUREMENT • Current design of beam dump (Default) • 160x160x160 cm3 iron block • Surrounded by 80 cm concrete • Assuming a conical collimator with 8 cm top diameter (and 12 cm base) consisting of 2 m iron and 1 m borated paraffin. • Assuming evacuated beam line till the dump. • Measure the average particle fluence 1.5-2 meters above floor from neutrons and photons (and charged particles) • Five time intervals for scoring (time-of-flight) • < 1 us, 1-10 us, 10-100 us, 100 us-1 ms, >1 ms • Production & transport thresholds • 500keV for e-e+ • 1 MeV for photons (to exclude 511 keV annihilation peak) IRON neutron beam: 200 eV-20 keV2 eV-200 eV Collimator not optimized!

  4. Background contributions Neutrons 10us – 100us (200eV – 20keV) Photons 10us – 100us Collimator not optimized!

  5. OPTIMIZATION Minimizing the beam dump backscattering by adding moderator and/or neutron absorber. Combining borated paraffin (BPE)and boron carbide (B4C). 15 cm BPE5 cm B4C 20 cm BPE Optimal combination: 5 cm B4C and 15 cm BPE 20 cm B4C

  6. OPTIMIZATION Minimizing the beam dump backscattering using a pencil beam sampled from the real neutron beam profile. Drilling a hole in the iron block to induce more scattering in iron. Combine with moderating/absorbing materialsborated paraffin (BPE)and boron carbide (B4C). Decreased tube 10cm capture) 20 cm inlet Combi inlet20 Combi inlet20 B20 Combi layer + 40 cm inlet

  7. COMPARING DESIGNS with default configuration Profiles 20 cm from the beam, 1.5 – 2 m above floor

  8. SUMMARIZED PLOTS Neutrons Neutron fluence [n/7e12 ppp] Photons > 1 MeV Distance from beam centre [cm] 10 us – 100 us (primary beam energy 200 eV – 20 keV) Photon fluence [g/7e12 ppp] Distance from beam centre [cm]

  9. CHARGED PARTICLES 10 us – 100 us e-e+ > 500 keV Charged particle fluence [chp/7e12 ppp] Bad statistics but there is a systematic decrease Distance from beam centre [cm]

  10. SUMMARY • Dump design • Extending the tube inside the dump to reduce (fast arriving) neutronand photonbackscattering. • Combining borated paraffin andboron carbide to moderate and absorb neutrons. • Extending boron carbide through the roof to absorb more backscattered particles. • Further simulations • Check radiation dose limits outside bunker (RP) with the optimized design. • Lower the EMF thresholds and check contributions from capture gammasfrom 10B(n,α)7Li* reactions.

  11. Complete plots

  12. Neutron background < 1 us 1 us – 10 us 1 us – 10 us 10 us – 100 us 100 us – 1 ms

  13. Photon background < 1 us 1 us – 10 us 1 us – 10 us 100 us – 1 ms 10 us – 100 us

  14. Charged particles background < 1 us 1 us – 10 us 100 us – 1 ms 1 us – 10 us 10 us – 100 us

  15. Cons when removing iron: Expensive to modify iron block, outside radiation still under acceptable limits? But as these plots show the scattering in iron is essential to reduce the backscattering of high energy neutrons. Therefore we need to extend the tube inside the iron block.(It is also shown that extending the paraffin is unnecessary.) Bouchon 1 Bouchon 2 Bouchon 3 Bouchon 3* Combi inlet 20 10 us – 100 us (200 eV – 20 keV) 1 us – 10 us (20 keV – 2 MeV)

  16. Neutron background in EAR-2 < 1 us (beam > MeV) 1 us – 10 us (beam keV-MeV) 1 us – 10 us (beam < eV) 10 us – 100 us (beam ~keV) 100 us – 1 ms (beam ~eV)

  17. Photon background in EAR-2 < 1 us 1 us – 10 us 100 us – 1 ms 10 us – 100 us 1 us – 10 us

  18. Charged particles background in EAR-2 < 1 us 1 us – 10 us 10 us – 100 us 100 us – 1 ms 1 us – 10 us

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